International trade deals are incredibly complicated, and often come down to minute details about specific products or services. In the case of a potential U.S-U.K. trade deal, it appears as if a major sticking point might be chicken.

Liam Fox, Britain’s international trade minister, is in Washington Monday for talks on the potential deal. The heat is on Fox from backers of Brexit; they want him to prove that Britain can make bilateral trade deals outside of the framework of the European Union.

To get the deal done, however, U.S. negotiators are making one key demand: American farmers wants to export cheap, chlorine-washed chicken to the United Kingdom. Right now, such exports are banned under EU rules.

A spokesperson for British Prime Minister Theresa May said it was too early to get into “specifics” or “hypotheticals” on what a possible trade deal with the United States would look like. Downing Street also said that food safety was among the highest priorities for British negotiators.

However, a source close to Fox told the U.K.’s Telegraph that “Americans have been eating it perfectly safely for years” and that any “meaningful” trade deal with the United States would have to include agriculture, even if British farmers object.

Those opposed to Britain’s decision to leave the EU are seizing on the poultry issue, arguing the U.K. is agreeing to lower food standards in the first major, potential deal with a foreign power.

“This row about chlorine chicken is a direct result of the government’s decision to leave the single market,” Ben Bradshaw, a Labour MP who is opposed to a hard Brexit, told the Guardian. “They are so desperate for new trade deals to make up for some of the losses that they seem ready to compromise on the safety of the food we eat.”

Fox, for his part, was cagey when asked about the chicken issue. After speaking at the American Enterprise Institute in Washington, he refused to say whether he would eat a bird washed in chlorine.

“The British media are obsessed with chlorine-washed chickens, a detail of the very end stage of one sector of a potential free trade agreement,” Fox said, according to the Sun. “I say no more than that.”